Microfluidic devices are used to manipulate and precisely dispense defined microscopic volumes of liquid inside micro-sized structures. For example, a tab-based titration system may include a microfluidic pump that is programmed to dispense a fixed volume of reagent onto a well plate. In that case both the amount of liquid to dispense and the time taken to dispense may be fixed to define a fluid flow rate for the system.
A microfluidic pump may also be used to dispense a respiratory drug to a patient. In that case, the way the patient uses the pump represents a non-constant external variable. The amount of drugs to be administered to the patient at any particular time may not be constant and, for that reason, the most effective means for delivering a defined dose may not be a fixed flow rate. A more effective method for delivering the dose, in that case, would be to adjust the amount of medicament being dispensed based on the patient's behavior. In that case, when the user's inhale force is greater, the flow rate increases to deliver more fluid. On the other hand, when the user's inhale force is lighter, the flow rate decreases to deliver less fluid.
Microfluidic pumps are also used in inkjet printing. In an inkjet printing application, the output flow rate of ink is variable. The flow rate is often determined by a thermal ejector chip, which may dispense ink directly across an air path onto a paper substrate. Traditionally, the ink flow rate is controlled by adjusting the number of heaters selected for firing along with the firing rate for each element. However, this process required multiple digital inputs, which had to be updated for each firing cycle. While this level of control may be necessary for printing applications, it adds complexity and cost to these microfluidic devices and, for at least these reasons, is not optimal for all applications.
There is a need for a microfluidic device which can be activated and controlled, including the ability to adjust the flow rate, in order to deliver a prescribed amount of fluid with a minimal number of inputs.
The present disclosure advantageously provides a microfluidic pump for carrying out a firing sequence to eject a fluid where the flow rate may be varied based on a variable analog input.
In one aspect, the microfluidic pump includes a fluid supply source for supplying a fluid, a firing chamber for carrying the fluid supplied by the fluid supply source. The firing chamber includes a nozzle that is in fluid communication with the firing chamber. A firing mechanism in fluid communication with the firing chamber ejects fluid out of the firing chamber through the nozzle during a firing sequence. The firing sequence includes at least a firing step, where the firing mechanism is activated and fluid is ejected from the firing chamber as a result of the firing mechanism activating, followed by a wait step, where the firing mechanism is deactivated for providing a time delay between subsequent firing steps.
The pump also includes a power circuit in electric communication with the firing mechanism for activating and deactivating the firing mechanism in response to a control signal. A logic circuit, in electric communication with the power circuit, send a control signal to the power circuit. The control signal controls the length of time of each step in the firing sequence. The control signal is dependent on a predetermined fixed frequency signal and it controls the firing step. The control signal may also be dependent on a variable frequency signal to control the wait step.
The predetermined fixed frequency signal and the variable frequency signal are provided by a first and second oscillator, respectively. The first oscillator is in electric communication with the logic circuit and sends a predetermined fixed frequency signal to the logic circuit. The fixed frequency signal is a series of timing pulses, wherein each pulse is separated by a fixed time interval. The second oscillator is in electric communication with the logic circuit and sends a variable frequency signal to the logic circuit. The variable frequency signal is a series of timing pulses wherein each pulse is separated by a variable time interval.
The pump also includes a first input for providing a variable input signal to the second oscillator. The second oscillator varies the interval of time separating each pulse of the series of timing pulses of the variable frequency signal according to the variable input signal from the first input. The logic circuit is configured to vary the control signal according to the frequency of the variable frequency signal from the second oscillator to thereby vary the length of the wait step and, as a result, vary the time between ejections of fluid from the firing chamber.